Where as figs in the open will only ripen one crop of fruit a year, those in a heated greenhouse can ripen two. With sufficient heat it is even possible to secure three crops a year, but this is a heavy drain on the strength of the tree and expensive in fuel consumption as it is necessary to start growth in December with a temperature of 65-70°F (18-21°C), gradually rising to 80°F (27°C).
The fig is most conveniently trained as a fan against the wall of a lean-to house. The soil in the border should not be rich as this would encourage growth at the expense of fruit—a very average loam will serve. Indeed, to keep growth within the confines of even a fair-sized greenhouse it is advisable to restrict the roots, doing this by making up the border inside a concrete 'box'. Wooden shuttering should be used to make a bottomless box, 1.3m (4ft) long by 0.6m (2ft)wide and 0.6m (2ft) deep. When the concrete has set hard, dig out a little soil from the bottom and replace with a layer of broken brick or stone, well rammed in place, so that free drainage is possible but the formation of tap-roots discouraged.
Fill this box with light soil, adding sand or brick or mortar rubble if the natural soil in the garden is not sandy or gravelly. Do not add manure.
Turn on the heat to start growth in February with a temperature around 55-60°F (13-16°C). The border will need flooding at the start of the season and plenty of water will be required when the tree is in full growth. It helps growth (and deters red spider mites) to damp down the path and syringe the foliage regularly front bud break until the autumn, withholding the spray while the fruit is ripening.
When the second crop has been picked, probably in September, gradually cut down the water supply and, when all the leaves have dropped, let the tree rest, with free ventilation, no heat and the minimum amount of moisture. Close the house during frost and give a little warmth only when conditions are severe and the temperature inside the house is likely to fall below freezing point.
Pruning and disbudding follow similar lines as for outdoors figs but it should be remembered that the second (autumn) crop is borne on the new wood made that spring and summer. Embryo figs on the tips of the new growths will give the next season's spring crop. Therefore, there must be no summer pinching of new shoots.
As with peaches, red spider mites may be a nuisance on figs under glass, particularly if conditions have been too dry. Scale insects can also give trouble but remember that it is not safe to deal with these by applying tar-oil winter wash during the dormant period as the tender, embryo figs would be harmed. In bad cases a summer petroleum wash may be used but it is generally better to attempt hand control using a stiff brush to remove the offending brown scale-like insects.
Any of the fig varieties normally recommended for the open may be grown under glass—Brown Turkey', 'Brunswick' and 'White Marseilles', for instance--but with heat available the choice is widened. `Bourjassotte Grise', 'Negro Largo' and `Violette Sepor' are all good.